The present invention relates to a receiver capable of adaptively taking phase synchronization with high accuracy for a modulated signal in which sub-carriers are multiplexed, such as an OFDM (Orthogonal Frequency Division Multiplexing) system.
One example of this kind of conventional receiver is described in JP-A-95174/1995. FIG. 13 is a block diagram of its apparatus for demodulating an OFDM signal. This apparatus detects a phase difference from a modulation result of an arbitrary carrier in order to conduct phase synchronization for a modulated signal in which sub-carriers are multiplexed.
In FIG. 13, 1000-1-1000-n are input terminals, 1001 is a fast Fourier transform (FFT) circuit of n points, 1002 is a parallel/serial transform circuit, 1003 is a selector, 1004 is a phase difference detector, and 1005 and 1006 are output terminals.
Serial/parallel transformed n received signals are input to the FFT circuit 1001 of n points through the input terminals 1000-1-1000-n. The FFT circuit 1001 applies Fourier transformation to the input signals and de-multiplexes sub-carriers therefrom, and inputs the sub-carriers to the parallel/serial transform circuit 1002.
The parallel/serial transform circuit 1002 applies parallel/serial transform to each of the input sub-carrier components and outputs it to the output terminal 1005, and also, outputs it to the selector 1004. Furthermore, the parallel/serial transform circuit 1002 outputs to the selector 1003 a pulse for indicating time when each subcarrier component is output.
The selector 1003 selects a sub-carrier component to be input, based on the input pulse, and outputs it to the phase difference detecting circuit 1004.
In the phase difference detecting circuit 1004, assuming that a phase of a symbol under ideal condition in which phase synchronization is established is a reference phase, a difference between the input sub-carrier component and the reference phase is detected as a phase error, and it is output to the output terminal 1006. The phase error output to the output terminal 1006 is integrated by a loop filter and so forth, and is fed back to a local oscillator.
However, in the above-mentioned conventional OFDM signal demodulating apparatus, there is a task that it becomes to be difficult to detect a correct phase difference when distortion occurs in the selected sub-carrier component due to disturbance such as a noise in a communication line.
Also, in JP-A-95174/1995, although it is suggested to adaptively select a sub-carrier based on a noise and distortion, a method and an arrangement therefor are not disclosed.
The present invention is made to solve the above-mentioned problems.
Moreover, the objective of the invention is to provide a receiver for receiving a modulated wave in which a plurality of sub-carriers are multiplexed, to provide the receiver for conducting phase tracking with high accuracy, and capable of obtaining high reception characteristic.
In a receiver for receiving a modulated wave for carrying a data in which N sub-carriers are multiplexed, the receiver of the first present invention has a sub-carrier demodulating circuit for receiving the above-described plurality of (k, 1xe2x89xa6kxe2x89xa6N) sub-carrier components which are multiplexed and de-multiplexed, and outputting a result of demodulating each of the above-described sub-carrier components as a demodulation result of each of the above-described plurality of sub-carrier components, and for conducting determination based on the above-described demodulation result and outputting a determination result, and also, outputting a distortion correction coefficient for each of the above-described plurality of sub-carrier components, and a value which is generated by correcting each of the above-described plurality of sub-carrier components based on the above-described distortion correction coefficient, and a phase estimating circuit for receiving the determination result of each of the above-described plurality of sub-carrier components, the distortion correction coefficient for each of the above-described plurality of sub-carrier components, and the value which is generated by correcting each of the above-described plurality of sub-carrier components based on the above-described distortion correction coefficient, and for outputting a phase error.
For example, the phase estimating circuit of the first present invention has k phase comparison circuits for receiving the determination result of each of the above-described plurality of sub-carrier components and the value which is generated by correcting each of the above-described plurality of sub-carrier components based on the above-described distortion correction coefficient, and for detecting a phase difference between the above-described corresponding demodulation result and the value corrected based on the above-described distortion correction coefficient, and outputting it as a phase difference of each sub-carrier, k electric power detecting circuits for receiving the distortion correction coefficient for each of the above-described plurality of sub-carrier components, detecting electric power of the distortion correction coefficient for each of the above-described plurality of sub-carrier components, and outputting it as distortion correction coefficient electric power of each sub-carrier, k weight setting circuits for receiving each distortion correction coefficient electric power of the above-described each sub-carrier, and based on the distortion correction coefficient electric power of the above-described each sub-carrier, for obtaining a weight for the above-described each sub-carrier for weighting a phase difference of the above-described each sub-carrier and conducting synthesis thereof, and outputting the weight, and a weighting and synthesizing circuit for outputting a result of weighting and synthesizing a phase difference of the above-described each sub-carrier based on the weight for the above-described each sub-carrier as a phase error.
For example, the above-described weight setting circuits of the first present invention make a weight for weighting to be large if the distortion correction coefficient electric power of the above-described each sub-carrier is small, and make a weight for weighting to be small if the distortion correction coefficient electric power of the above-described each sub-carrier is large.
For example, the above-described weight setting circuits of the first present invention set a weight to be 1 if the distortion correction coefficient electric power of the above-described each sub-carrier is smaller than a determined threshold value, and set a weight to be 0 if the distortion correction coefficient electric power of the above-described each sub-carrier is larger than a determined threshold value.
In a receiver for receiving a modulated wave for carrying a data in which N sub-carriers are multiplexed, the receiver of the second present invention has a sub-carrier demodulating circuit for receiving the above-described plurality of (k, 1xe2x89xa6kxe2x89xa6N) sub-carrier components which are multiplexed and de-multiplexed, and outputting a result of demodulating each of the above-described sub-carrier components as a demodulation result of each of the above-described plurality of sub-carrier components, and for conducting determination based on the above-described demodulation result and outputting a determination result, and outputting a value which is obtained by correcting distortion generated in each of the above-described plurality of sub-carrier components, and a phase estimating circuit for receiving the determination result of each of the above-described plurality of sub-carrier components, the value which is obtained by correcting distortion generated in each of the above-described plurality of sub-carrier components, and the above-described plurality of sub-carrier components which are multiplexed and de-multiplexed, and for outputting a phase error.
For example, the phase estimating circuit of the second present invention has k phase comparison circuits for receiving the determination result of each of the above-described plurality of sub-carrier components and the value which is obtained by correcting distortion generated in each of the above-described plurality of sub-carrier components, detecting the above-described corresponding demodulation result and the value which is obtained by correcting distortion generated in each of the above-described plurality of sub-carrier components, and outputting them as a phase difference of each sub-carrier, k electric power detecting circuits for receiving the above-described plurality of sub-carrier components which are multiplexed and de-multiplexed, detecting electric power of the above-described plurality of sub-carrier, components which are multiplexed and de-multiplexed, and outputting it as electric power of each sub-carrier component, k weight setting circuits for receiving each electric power of the above-described each sub-carrier component, and based on the electric power of the above-described each sub-carrier component, for obtaining a weight for the above-described each sub-carrier for weighting a phase difference of the above-described each sub-carrier and conducting synthesis thereof, and outputting the weight, and a weighting and synthesizing circuit for outputting a result of weighting and synthesizing a phase difference of the above-described each sub-carrier based on the weight for the above-described each sub-carrier as a phase error.
For example, the weight setting circuits of the second present invention make a weight for weighting to be small if the electric power of the above-described each sub-carrier component is small, and make a weight for weighting to be large if the electric power of the above-described each sub-carrier component is large.
For example, the weight setting circuits of the second present invention set a weight to be 0 if the electric power of the above-described each sub-carrier component is smaller than a determined threshold value, and set a weight to be 1 if the electric power of the above-described each sub-carrier component is larger than a determined threshold value.
In a receiving method of receiving a modulated wave for carrying a data in which N sub-carriers are multiplexed, said receiving method comprises the steps of:
receiving a plurality of (k, 1xe2x89xa6kxe2x89xa6N) sub-carrier components which are multiplexed and de-multiplexed, and outputting a result of demodulating each of said sub-carrier components as a demodulation result of each of said plurality of sub-carrier components,
conducting determination based on said demodulation result and outputting a determination result, and outputting a distortion correction coefficient for each of said plurality of sub-carrier components, and a value which is generated by correcting each of said plurality of sub-carrier components based on said distortion correction coefficient; and
estimating a phase error based on said determination result of each of said plurality of sub-carrier components, said distortion correction coefficient for each of said plurality of sub-carrier components and said value which is generated by correcting each of said plurality of sub-carrier components based on said distortion correction coefficient.
In the receiving method, wherein said step of estimating a phase error comprises the steps of:
receiving the determination result of each of said plurality of sub-carrier components and the value which is generated by correcting each of said plurality of sub-carrier components based on said distortion correction coefficient, and for detecting a phase difference between said corresponding demodulation result and the value corrected based on said distortion correction coefficient, and outputting it as a phase difference of each sub-carrier;
receiving the distortion correction coefficient for each of said plurality of sub-carrier components, detecting electric power of the distortion correction coefficient for each of said plurality of sub-carrier components, and outputting it as distortion correction coefficient electric power of each sub-carrier;
receiving each distortion correction coefficient electric power of said each sub-carrier, and based on the distortion correction coefficient electric power of said each sub-carrier, for obtaining a weight for said each sub-carrier for weighting a phase difference of said each sub-carrier and conducting synthesis thereof, and outputting the weight; and
outputting a result of weighting and synthesizing a phase difference of said each sub-carrier based on the weight for said each sub-carrier as a phase error.
In the receiving method, wherein said step of obtaining a weight make a weight for weighting to be large if the distortion correction coefficient electric power of said each sub-carrier is small, and make a weight for weighting to be small if the distortion correction coefficient electric power of said each sub-carrier is large.
In the receiving method, wherein said step of obtaining a weight set a weight to be 1 if the distortion correction coefficient electric power of said each sub-carrier is smaller than a determined threshold value, and set a weight to be 0 if the distortion correction coefficient electric power of said each sub-carrier is larger than a determined threshold value.
In a receiving method of receiving a modulated wave for transmitting a data in which N sub-carriers are multiplexed, said receiving method comprises the steps of:
receiving a plurality of (k, 1xe2x89xa6kxe2x89xa6N) sub-carrier components which are multiplexed and de-multiplexed, and outputting a result of demodulating each of said sub-carrier components as a demodulation result of each of said plurality of sub-carrier components,
conducting determination based on said demodulation result and outputting a determination result, and outputting a value which is obtained by correcting distortion generated in each of said plurality of sub-carrier components; and
estimating a phase error based on said demodulation result of each of said plurality of sub-carrier components, said value which is obtained by correcting distortion generated in each of said plurality of sub-carrier components and said plurality of sub-carrier components which are multiplexed and de-multiplexed.
In the receiving method, wherein said step of estimating phase error comprises the steps of:
receiving the determination result of each of said plurality of sub-carrier components and the value which is obtained by correcting distortion generated in each of said plurality of sub-carrier components, detecting said corresponding demodulation result and the value which is obtained by correcting distortion generated in each of said plurality of sub-carrier components, and outputting them as a phase difference of each sub-carrier;
receiving said plurality of sub-carrier components which are multiplexed and de-multiplexed, detecting electric power of said plurality of sub-carrier components which are multiplexed and de-multiplexed, and outputting it as electric power of each sub-carrier component;
receiving each electric power of said each sub-carrier component, and based on the electric power of said each sub-carrier component, for obtaining a weight for said each sub-carrier for weighting a phase difference of said each sub-carrier and conducting synthesis thereof, and outputting the weight; and
outputting a result of weighting and synthesizing a phase difference of said each sub-carrier based on the weight for said each sub-carrier as a phase error.
In the receiving method, wherein said step of obtaining a weight make a weight for weighting to be small if the electric power of said each sub-carrier component is small, and make a weight for weighting to be large if the electric power of said each sub-carrier component is large.
In the receiving method, wherein said step of obtaining a weight set a weight to be 0 if the electric power of said each sub-carrier component is smaller than a determined threshold value, and set a weight to be 1 if the electric power of said each sub-carrier component is larger than a determined threshold value.
In the present invention, weighting based on a coefficient for correcting distortion generated in each sub-carrier is conducted for a demodulation result of each sub-carrier and a phase error of determination signal points. For example, a distortion correction coefficient for a sub-carrier in which large attenuation distortion occurs in a communication line becomes to be a large value so as to correct the attenuation distortion. On the other hand, a correction coefficient for a sub-carrier component in which distortion does not occur in a communication line becomes to be a value close to 1.
In this manner, by conducting the weighting for a phase error of each sub-carrier, which is proportional to an inverse number of a distortion correction coefficient, influence of a noise is suppressed, and the present invention is equivalent to adaptively selecting a sub-carrier in which a noise component is less and to conducting phase synchronization.